Method of die stamping and drawing



Dec. 29, 1953 w. J. BENTSEN 2,664,062

METHOD OF DIE STAMPING AND DRAWING I Filed April 28, 1947 2 Sheets-Sheet l 5/ -1 3 Q 1x, a g m INVENTOR J. BENTSEN ATTORNE] Dec. 29, 1953 w. J. BENTSEN 2,664,062

METHOD OF DIE STAMPING AND DRAWING Filed April 28, 1947 2 Sheets-Sheet 2 f'y' 14A ATTORNEY Patented Dec. 29, 1953 UNITED STATES PATENT OFFICE 2,664,062 ME'iIioD'oF DIE STAMPING AND DRAWING William Bentsen, San Diego, Calif assignor to Solar Aircraft Company, San Diego,.Calif., a iirpo'ra'tion of Califernia Application pril 28', 1947, Serial No. 744374 1 Claim. 1

This invention relates to the art of shaping sheet metal between ceihplefnentary dies and is particularly useful in connectionwith' shapes involving a steep portionsurmounted by a flat'por tion which merges into the steep portion at a sharp shoulder. With the methods heretofore used, there has beena pronounced thinning of the metal at and adjacent the shoulder, and an object of the invention to reduce or eliminate excessive local thinning of the metal.

Another object is to provide a method of producing a thickening of the metal in a die stamp ing at desired local areas;

This is a ccntinuatioiiin part of my applica= tion Serial No;'616,86'9, -filed September 17, 1945, now Patent No. 23959102, issued'January 24, 1950.

Briefly, I accomplish the foregoing objects by preshaping the metal sheet, prior to placingit between the final die's',-in' such a way as to" provide a bulge, or wrinkle, in the sheet ator adjacent the area that'would otherwise be exces sively thinned. The b'ulg'e, or wrinkles, causes the sheetto have a greater absolute area locally in the region where" the final dies would normally stretch and thin the metal excessively. By suit ably controlling the extent and position of the bulge, the thinning of-the metal that would th erwise occurcanbe-partially, fully, or over, compensated for. Over-compensation produces an actual thickening-=01 the sheet and is" desirable where local reinforcement is advantageous.

Such local thickening forreinforcing'purposes is highly desirable insuch' structures as aircraft exhaust manifolds where long life without excessive weight is an objective. such instances the local areas that can desirably be thickened are those exposedto the-highest temperatures and to the highest impact of corrosivegases.

Experience shows that stamped manifold structures repeatedly fail at-thesame points, and failures can be reduced by' thickening the'wa-ll-at such points in accordance with the present invention. W

It was found that failures in welded sheet metal manifolds frequently occurred at points adjacent the welds when the-stainpinghad been thinned at those points in thestamping operation. The thickening ofthe metaladjacent thewelds in accordance with the present invention'hasma terially reduced the incidence of such failures;

As examples ofpointsinmanifold structures that are benefited by: thickening, because of ';ex-" posure to high temperatures-andgas impinge ment, are the'sidesofcbllector ringsnimmedi ately oppositetheengine-ports, and the down:

stream outer sides ofsharp elbows. Thickening of such points produces more even expansion;

As examples of points in manifold structures that are benefited by thickening because of ex posure to extra stresses, are the rigidly secured port legs of collector rings, where the ring is supported by the port legs; The invention is particularly useful where the collector rings are made up of independent, slidably connected sections mounted as" cantilevers from the exhaust ports of an engine.

The shape and extent of the bulge or wrinkles produced in the preliminary shaping operation must be carefully controlled, else wrinkling of the sheet will beproduced inthe final dies, and there are disclosed herein procedures; for preparing, from the final dies, preliminary dies that will impartthe necessary bulgeor wrinkles to the sheet; In accordance with one proce duremne of the two complementary final dies" is'alt'ered by superimposing on certain areas thereof a dome or ridge of plastic material such asfclay," and then using the altered die as a pattern from which to pre pare a pair ofcomplementary preliminary dies which the sheet is Dres'haped. After preshaping in the preliminary eie'sthe sheet ha s a bulge which provides excessi reaat a local point as compared to'the areas or the juxtapesed portions of the finaldie, so that during final closing move ment of the final diesfon'the sheet the bulged area is either stretehedto'a lesser extent than it would be if it had not beenpreshabed, 61* is actually compressed 56 that its thickness is in creased. a

The present in iffiti oh is particularly useful connection with the invention of Burger and Skinner, Patent No. 2,383,706; issued Assesses, 1945, and entitled Method of Making Preli'ini nary Shaping Dies The procedure describedin' the Burger and Skinner" patent involves the mak,-' ing' of a preliminary die'ifih' annal the were forming on the surface of the final diea substantially non-compressible and non-stretchable wax form, removing the form fro nthe final die, flattening' it to a suitable extent without materially altering its absolute area, and then usingit as pattern for the preliminary dies. The prd i li in accordance withthe presentinyention differs from that of the Burger-and Skinner that the non-compressible andnon-stretchabl pattern is formed on the original die after the latter has been altered: by the addition of the clay dome or ridge, ,insteadof constructing it directly on the original die:

In the drawing:

Fig. 1 is a perspective view of a section of an exhaust collector ring or manifold such as is used on radial airplane engines;

Fig. 2 is a die pattern in accordance with the present invention for forming the back half stamping of the manifold section shown in Fig. 1;

Fig. 3 is a cross section showing a portion of a manifold made from two half stampings prepared by a prior art process;

Fig. 4 is a cross section corresponding to Fig. 3 but showing a portion of a manifold made from stampings prepared by the present process;

Fig. 5 is a cross section taken in the plane V-V of Fig. 2, showing a wax pattern formed in the die pattern of Fig. 2;

Fig. 6 is a section in the same plane as Fig. 5, showing the wax pattern reformed;

Fig. 7 is a sectional view taken in the plane corresponding to that of Fig. 5 but showing a stamping formed from the wax pattern of Fig. 6 in the process of being shaped between final dies;

Fig. 8 is a view similar to Fig. 7 showing the dies fully closed;

Fig. 9 is a cross section similar to Fig. 5, but taken in the plane IXIX of Fig. 2;

Fig. 10 is a section in the same plane as Fig. 9, showing the wax pattern reformed;

Figs. 11 to 15 are sectional views taken in a plane corresponding to plane XIXI of Fig. 2, showing successive steps in the prior art process for comparison with the present process; and

Figs. 11A to 15A are views corresponding to Figs. 11 to 15, respectively, but illustrating corresponding successive steps in accordance with the present invention.

Referring to Fig. 1, there is shown a manifold section that may consist of two matched half stampings welded together. The section has a rigid port leg 26 and an expansible port leg 21, the two legs being secured to adjacent cylinders of a radial engine. At its two opposite ends, the section 25 may slidably engage similar adjacent manifold sections.

Manifolds of this type are subjected to differential temperature stresses, the hottest points thereof being the areas marked 28 because of their positions directly opposite the port legs 26 and. 21 as a result of which they must redirect the hot gases toward the exit end 29 of the section. The reentrant corners 30 are also subject to severe strains due to thermal expansion, because the thin sheet metal of the manifold section lengthens more than does the distance between the engine ports due to expansion of the engine.

Another highly stressed portion of the manifold is the rigid cantilever port leg 26, for it must transfer the stresses set up by vibration of the section 25, and these stresses are often built up to considerable amplitudes by harmonic vibration of the engine.

As has been previously indicated, it has been customary to form manifold sections such as the section 25 by welding together two mating half stampings. The general shape of one of the half stampings is illustrated in Fig. 2 which discloses a die pattern 3|a for one of the half stampings, in this instance, the rear half stamping of the manifold section 25. The half stampings, as they come from the die, have diametrical flanges which are subsequently trimmed off before the edges of two mating half stampings are welded together. Thus the flanges of the two stampings shown welded together in Fig. 3 have 4 been trimmed off at the dotted line 45, 45. The weld metal joining the two half stampings is indicated at 46.

Fig. 3 illustrates a structure formed in accordance with the practice of the prior art and it will be observed that both stampings are thinned excessively adjacent the weld as shown at 36, 35.

It is found that in service the thin portions 36 adjacent the seam run hotter than other portions, and, for this reason, suffer more rapid corrosion, with the result that they eventually become thinned to an even greater extent, as shown by the dotted lines 43 in Fig. 3. The reason why the prior art production methods produced the thinning as indicated at 36 will now be explained with reference to Figs. 11 to 15, inclusive.

The best prior art practice known to me is that disclosed in the patent to Burger et al. 2,383,706 which discloses a practical method of making a preliminary die from a final die for the better production of relatively deep stampings.

Referring first to Fig. 11, there is shown the plaster pattern 3|a for the lower or female final die section 3|, in which the stamping is to receive its final shaping. In accordance with the practice taught in the Burger et al. patent, a flexible wax pattern reinforced with cheesecloth, and indicated at 33 in Fig. 11, is formed directly over the die pattern 3 la so that it conforms exactly with the shape thereof. This flexible pattern 33 is then removed from the die pattern 3m and is flattened, without materially changing its absolute area. The resultant change is indicated in Fig. 12. It will be noted from inspection of Fig. 12 that the pattern no longer falls entirely Within the confines of the final die 3|, the edges of which are indicated in dotted lines. The wax pattern, after being flattened, as indicated in Fig. 12, is then used to form a preliminary stage die, in accordance with the teachings of the Burger et al. patent, and from these preliminary dies a metal sheet 34 (Fig. 13) corresponding in shape to the pattern 33 is produced. Fig. 13 shows this sheet 34 positioned between the final die 3| and the punch 32 therefor. It will be observed from inspection of Fig. 13 that the lowermost portion of the punch 32 is engaging the sheet metal blank 34 near the middle thereof, and that the sharp edges 35 of the die 3| are engaging the blank 34 and supporting it. During subsequent closing movement of the punch 32 the sharp edges 35 of the die 3| bind against the metal blank 34, causing the metal of the blank to be stretched and thinned adjacent the flanges as shown in Figs. 14 and 15.

A purpose of the present invention is to prevent the thinning of the metal near the seam as indicated at 35 in Fig. 3, and produce a manifold section of substantially uniform thickness throughout, as shown in Fig. 4. The practice in accordance with the present invention whereby this result is obtained will now be explained with reference to Figs. 11A to 15A inclusive.

First, beads 31, 41, 51, and 61 (Fig. 2) are formed along the edges of the opening in the final die 3| or the corresponding plaster pattern 3|a. Those portions of the beads in the plane XI-XI of Fig. 2 are shown in the sectional view of Fig. 11A from which it will be observed that the two beads 31 and 41 are of substantially the same shape and dimensions and have their inner edges flush with the edges of the die cavity. These beads may be formed of various plastic materials but it has been found very satisfactory to .use

clay. After the beads have hardened sufllciently. the Wax pattern 33a. is formed thereon exactly as previously described with reference to Fig. 11.. It will be observed that in Fig. 11A the underside of the wax pattern 33c follows the curved line 35, 38, 39, instead of the straight line 35, 39 in Fig. This adds ar a to the. pattern alon th ed f. the avity.

The Wax pattern 33a is. removed from. h i pattern 31c and flattened asindicated in Fi 12 Fro this pattern, prelim nary d es are. t n m e an u d t f rm a sheet metal blank 3411 (Fi 18A) int the samev shape. This formed bla 4. s t en stamped between the final dies. successive stages of the stamping operation being shown in Figs. 13A, 14A, and 15A, respectively.

Although the stamping 34a as receivedfrom the preliminary dies may initially ride against the sharp edges 35 of the final die 3|, this occurs only while the sheet is relatively unconfined and free to move. When th punch 32 approaches the die 3| more closely, as shown in Fig. 13A, the flat surfaces 30 of the punch 32 make contact with the bulges 42 of the preformed sheet 34a, forcing the lowermost curved portion of the blank 34a in compressive contact with the bottom of the die cavity. As the punch 32 continues to move into the die 3| as shown in Figs. 14A and 15A, the bulges 42 of the blank tend to flatten out and the metal is forced horizontally inwardly into the reentrant corners 4| of the punch 32. This lateral movement of the blank actually carries the undersurface thereof away from the sharp edges 35 of the die 31, and during the latter part of the stamping operation, from the instant that the bulges 42 come in contact with the punch 32, the operation is a compression forming operation rather than a drawing operation.

By judicious choice of the size of the beads 31, 41, et cetera, it is possible to keep the metal of the blank up to its original thickness, or in some instances to increase its thickness where that is desired.

A very important feature of the invention is that the metal can be forced into the reentrant corners 4! (Figs. 14A and 15A) to a considerably sharper radiu than the actual metal thickness. The results of the process in forming manifolds of nearly constant cross section near the weld seam are illustrated in Fig. 4.

There are other areas of the manifold structure shown in Fig. 1 in which it is advantageous to maintain thickness or actually increase the thickness. As previously mentioned, the areas 28 (Fig. 1) opposite the onrushing gas from the port legs would normally be hotter than the surrounding portion. Figs. to 8, inclusive, show how the thickness can be increased in the area 28 in accordance with the present invention.

Thus refer-ring to Fig. 5, it will be observed that in the section V--V of the area 28 (Figs. 1 and 2) the head 31 is considerably larger than the bead 51, and larger than the bead 31 in the section XIXI previously discussed.

The wax pattern 33a is then reformed in the areas adjacent the section VV as shown in Fig. 6. It will be observed that the extra area obtained in the wax pattern by the large bead 31 of Fig. 5 is not retained but is reduced approximately to the size of its counter bead 51 which in turn is comparable to the beads 31 and 41 in Fig. 11A. The remainder of the additional area is moved over into the portion desired to be thickened by manually forming in the Wax pattern 33a a plurality of undulations or corrugations 44,

which undulatlons arc reproduced in the metal blank formed with thepreliminar'y dies prepared fromithe' wax .patterm; -When the metal blank, having theundulations 44; therein, is pressed between thefinalpunchand 1314332 and 3| respec-. tively, as shown inFigs. .7, and 8, the undulations are pressed out of the metal, and since the metal has. no other place togothe section is. thickened in that region; The; thickening of the metal has been considerablyexaggerated in Fig. 8,, to make it apparent. Generallyit is only a few thousandths of an inch, and it is made possible by a slight shiftof the punch fl to the right in Fig. 8,

and by wear. of the dies where the metal is thickest. In the' stamping of stainless steel between dies -ofi relatively soft alloys, as is the general practice. dies wear-very rapidly at the areas where the steelis thickest, until substantially uniform pressures are exerted at all points.

While it would be possible to thicken the manlfold all the way around, as will be described later in connection with Figs. 9 and 10, it would not be desirable to do this in the sections of the areas 28 of Fig. 1. The purpose here is to distribute the metal of the manifold in such a way that there will be a nearly even temperature around the perimeter of any cross section, in spite of the fact that the gas may impinge on only a localized area of that cross section.

There are portions of the manifold structure shown in Fig. 1 in which it is desirable to thicken the entire perimeter of the cross section as compared with the section as a whole. Such an area is the cantilever port leg 26 because of the fact that the entire section 25 is cantilevered from the engine cylinder to which the port leg 26 is attached. Vibrational stresses are therefore greater in this port leg than in any other section of the manifold section, and it is desirable that the walls of the port leg increase in thickness as the port leg flange 26b is approached. As shown in Fig. 1, the port leg 26 is further reinforced by projections 26a extending from the flange 26b and welded to the port leg. However, even in addition to this, increased thickness of the walls is desired and this is obtained by making the beads 4'! and 51 (Fig. 2) of greater thickness in and adjacent the plane IX-IX of Fig. 2. This increased dimension of the beads 41 and 51 is clearly shown in Fig. 9. After the wax pattern 33a has been removed from the die 3|, the additional area that has been provided by the large beads 41 and 51 is transferred in part into undulations corresponding to the undulations 44 of Fig. 6, but extending over the entire curved portion of the wax sheet. When the resultant metal blank having corresponding undulations therein is pressed in the final die, it results in a substantial thickening of the metal over the entire section adjacent the plane IX-IX of Fig. 2, the thickness increasingas the end of the port leg is approached.

The invention has been explained by describing its application to the formation of one particular structural shape. Obviously the invention is useful in a variety of shapes and is therefore to be limited only to the extent set forth in the appended claim.

I claim:

In the art of stage forming sheet metal into a. final article having a longitudinally curved trough portion having longitudinally extending flanges joining the trough portion at sharp shoulders, the method comprising preforming the metal between preliminary mating dies to produce 7 longitudinally extending wrinkles in portions of said trough and to provide a bulge over a part of the flange portions closely adjacent said shoulders to provide excess metal at said wrinkles and said shoulders, and pressing the preformed sheet between mating final dies thereby placing said bulged portion and said wrinkles in said sheet in compression to prevent thinning in the stamping in the area adjacent said sharp shoulder and to thicken said trough at said wrinkles.

WILLIAM J. BEN'ISEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 469,785 Hart Mar. 1, 1892 511,392 White Dec. 26, 1893 Number Number Name Date Barthels Aug. 28, 1900 Merrill Mar. 26, 190 Thiem Dec. 26, 1905 Zerk May 15, 1917 Pribil May 14, 1918 Vorsmann July 18, 1922 Karmazin Jan. 15, 1929 Tarbox Jan. 3, 1933 Benedict Apr. 30, 1935 Graf Jan. 18, 1938 Vehko July 18, 1939 Stall et a1 Mar. 18, 1941 Burger Aug. 28, 1945 FOREIGN PATENTS Country Date Great Britain of 1897 

